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<STRONG>NAME</STRONG>
<STRONG>glLogicOp</STRONG> - specify a logical pixel operation for color
index rendering
<STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>
void <STRONG>glLogicOp</STRONG>( GLenum <EM>opcode</EM> )
<STRONG>PARAMETERS</STRONG>
<EM>opcode</EM> Specifies a symbolic constant that selects a logical
operation. The following symbols are accepted:
<STRONG>GL_CLEAR</STRONG>, <STRONG>GL_SET</STRONG>, <STRONG>GL_COPY</STRONG>, <STRONG>GL_COPY_INVERTED</STRONG>,
<STRONG>GL_NOOP</STRONG>, <STRONG>GL_INVERT</STRONG>, <STRONG>GL_AND</STRONG>, <STRONG>GL_NAND</STRONG>, <STRONG>GL_OR</STRONG>, <STRONG>GL_NOR</STRONG>,
<STRONG>GL_XOR</STRONG>, <STRONG>GL_EQUIV</STRONG>, <STRONG>GL_AND_REVERSE</STRONG>, <STRONG>GL_AND_INVERTED</STRONG>,
<STRONG>GL_OR_REVERSE</STRONG>, and <STRONG>GL_OR_INVERTED</STRONG>. The initial value
is <STRONG>GL_COPY</STRONG>.
<STRONG>DESCRIPTION</STRONG>
<STRONG>glLogicOp</STRONG> specifies a logical operation that, when enabled,
is applied between the incoming color index or RGBA color
and the color index or RGBA color at the corresponding
location in the frame buffer. To enable or disable the
logical operation, call <STRONG>glEnable</STRONG> and <STRONG>glDisable</STRONG> using the
symbolic constant <STRONG>GL_COLOR_LOGIC_OP</STRONG> for RGBA mode or
<STRONG>GL_INDEX_LOGIC_OP</STRONG> for color index mode. The initial value is
disabled for both operations.
____________________________________
| <EM>opcode</EM> | <EM>resulting</EM> <EM>value</EM> |
<EM>|</EM>_________________<EM>|</EM>_________________|
| <STRONG>GL_CLEAR</STRONG> | 0 |
| <STRONG>GL_SET</STRONG> | 1 |
| <STRONG>GL_COPY</STRONG> | s |
|<STRONG>GL_COPY_INVERTED</STRONG> | ~s |
| <STRONG>GL_NOOP</STRONG> | d |
| <STRONG>GL_INVERT</STRONG> | ~d |
| <STRONG>GL_AND</STRONG> | s & d |
| <STRONG>GL_NAND</STRONG> | ~(s & d) |
| <STRONG>GL_OR</STRONG> | s | d |
| <STRONG>GL_NOR</STRONG> | ~(s | d) |
| <STRONG>GL_XOR</STRONG> | s ^ d |
| <STRONG>GL_EQUIV</STRONG> | ~(s ^ d) |
| <STRONG>GL_AND_REVERSE</STRONG> | s & ~d |
|<STRONG>GL_AND_INVERTED</STRONG> | ~s & d |
| <STRONG>GL_OR_REVERSE</STRONG> | s | ~d |
| <STRONG>GL_OR_INVERTED</STRONG> | ~s | d |
<EM>|</EM>_________________<EM>|</EM>_________________|
<EM>opcode</EM> is a symbolic constant chosen from the list above.
In the explanation of the logical operations, <EM>s</EM> represents
the incoming color index and <EM>d</EM> represents the index in the
frame buffer. Standard C-language operators are used. As
these bitwise operators suggest, the logical operation is
applied independently to each bit pair of the source and
destination indices or colors.
<STRONG>NOTES</STRONG>
Color index logical operations are always supported. RGBA
logical operations are supported only if the GL version is
1.1 or greater.
When more than one RGBA color or index buffer is enabled for
drawing, logical operations are performed separately for
each enabled buffer, using for the destination value the
contents of that buffer (see <STRONG>glDrawBuffer</STRONG>).
<STRONG>ERRORS</STRONG>
<STRONG>GL_INVALID_ENUM</STRONG> is generated if <EM>opcode</EM> is not an accepted
value.
<STRONG>GL_INVALID_OPERATION</STRONG> is generated if <STRONG>glLogicOp</STRONG> is executed
between the execution of <STRONG>glBegin</STRONG> and the corresponding
execution of <STRONG>glEnd</STRONG>.
<STRONG>ASSOCIATED</STRONG> <STRONG>GETS</STRONG>
<STRONG>glGet</STRONG> with argument <STRONG>GL_LOGIC_OP_MODE</STRONG>.
<STRONG>glIsEnabled</STRONG> with argument <STRONG>GL_COLOR_LOGIC_OP</STRONG> or
<STRONG>GL_INDEX_LOGIC_OP</STRONG>.
<STRONG>SEE</STRONG> <STRONG>ALSO</STRONG>
<STRONG>glAlphaFunc</STRONG>, <STRONG>glBlendFunc</STRONG>, <STRONG>glDrawBuffer</STRONG>, <STRONG>glEnable</STRONG>,
<STRONG>glStencilOp</STRONG>
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